Centrifugal compressors convert mechanical energy provided by a driver, such as an electric motor, a gas turbine, a steam turbine or the like, into pressure energy for boosting the pressure of a gas processed by the compressor. A compressor essentially comprises a casing rotatingly housing a rotor and a diaphragm. The rotor can be comprised of one or more impellers, which are driven into rotation by the prime mover. The impellers are provided with blades having a broadly axial inlet section and a broadly radial outlet section. Flow channels are delimited by the blades and by a back plate or disc of the impeller. In some compressors, the impeller is provided with a shroud, opposite the back plate or disc, the blades extending between the back plate or disk and the shroud. Gas enters the flow channels of each impeller axially, is accelerated by the blades of the impeller and exit the impeller radially or in a mixed radial-axial fashion in the meridian plane. Accelerated gas is delivered by each impeller through a circumferentially arranged diffuser where the kinetic energy of the gas is at least partly converted in pressure energy, increasing the gas pressure.
The quantity of energy provided by the prime mover and absorbed by the compressor cannot be entirely converted into useful pressure energy, i.e. in pressure increment in the fluid, due to dissipation phenomena of various kinds involving the compressor as a whole.